Camera modules have been incorporated in a variety of consumer electronics devices, such as smart phones, mobile audio players, personal digital assistants, laptop and tablet computers, as well as desktop personal computers. A typical digital camera module is an assembly in which at least the following components have been integrated: a microelectronic imaging sensor integrated circuit chip, a printed circuit carrier such as a flexible circuit structure which carries power and signal connections between the sensor chip and other circuitry inside the consumer electronics device, and an optical system which includes a fixed focal length lens subsystem or autofocus lens subsystem. There may be additional optical elements such as infrared filters and neutral density filters. Typically, in most consumer electronics portable devices, such as smart phones and tablet computers, that have a relatively thin profile (or a so-called shallow z-height), the various optical path apertures in the optical system are of the fixed variety. That is in part because conventional variable apertures that use leaflets for example are not only complex (adding to the cost of the device as a whole) and more susceptible to physical shock or damage, but they also require additional headroom in the z-height direction, thereby leading to a thicker smartphone or tablet computer.
There has been a suggestion to use an electro-optic aperture in an imaging system, in order to avoid the use of moving parts while at the same time achieving improved focusing and greater depth of field. The electro-optic aperture may include an electro-chromic (EC) medium that attenuates light from the scene that is passing through the aperture, in response to a voltage being applied to a pair of transparent conductor layers between which the EC medium is sandwiched. An abrupt void or gap is formed in one of the transparent conductor layers, so as to form a ring-like aperture whose inner area remains transparent when the EC medium is energized and whose outer area becomes dark, thereby yielding in effect a smaller pupil. The electro-optic aperture may be positioned between a focusing lens of the system and the scene being imaged.